Ammonia (NH3) is one of the world's most important chemicals. In addition to its primary use in fertilizers, ammonia can also be used as an efficient coolant or a clean, effective fuel.
Manufacturing ammonia has remained surprisingly unchanged for over a century. The Haber-Bosch process has been the predominant process for making ammonia since the early twentieth century. The Haber-Bosch process involves using high pressures and temperatures in large, capital-intensive plants by combining nitrogen gas (N2) and hydrogen gas (H2) over an iron-based catalyst. Although the Haber-Bosch process has undergone decades of optimization, ammonia production still remains limited by thermodynamics to less than 20% conversion in a single pass. In order for Haber-Bosch plants to be economically viable, NH3 must be separated from unreacted N2 and H2, which must then be repressurized, reheated, and recycled. This requires tremendous capital expenditures and a large amount of energy. Haber-Bosch plants account for about 1.5% of global energy consumption. Moreover, the hydrogen gas is typically obtained by steam reforming of natural gas, which releases additional CO2 into the atmosphere.